1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a laser printer, or similar image forming apparatus, and more particularly to a charging device including a charging roller and a charging roller cleaning member for use in an image forming apparatus and a method of operating the device.
2. Discussion of the Background
In an image forming apparatus employing an electorophotography process, such as a copying machine, a facsimile, a laser printer, or the like, an increasing number of the image forming apparatuses are made compact by employing an electrophotographic image forming process cartridge wherein a photoreceptor, a developing device, a charging device, etc. are integrally accommodated in a case.
Many of the charging devices provided in such an electrophotographic image forming process cartridge employ a charging roller that contacts the photoreceptor with a pressure and uniformly charges a surface of the photoreceptor by applying a voltage to the charging roller. Typically, in such a charging device, a charging roller cleaning member made of, for example, a sponge or the like, slidably contacts a surface of the charging roller with an appropriate pressure. When the charging roller is rotated by rotation of the photoreceptor, the charging roller cleaning member removes foreign substances, such as toner and paper powder, from the surface of the charging roller, which are transferred onto the charging roller from the photoreceptor.
As an example of the above-described charging roller cleaning member, Japanese Laid-Open Patent Publication No. 7-325527 describes a cleaning roller that contacts a surface of a charging roller so as to clean the charging roller. The charging roller contacts a drum-shaped photoreceptor and is rotated by rotation of the photoreceptor. The cleaning roller includes a metallic core and a rubber layer covering a circumference of the metallic core. In addition, a string-shaped member formed of, such as, a sponge, a fiber material, or a soft rubber, etc. is spirally wound around the surface of the rubber layer. A length portion of the cleaning roller along an axial direction of the charging roller (i.e., a width portion of an effective cleaning area in an axial direction of the cleaning roller) is set to be greater than a charging contact width portion of the charging roller with the photoreceptor in the axial direction of the charging roller.
However, deterioration of the charging property of the charging roller typically tends to be caused when the above-described length portion of the cleaning roller is set to be equal to or greater than the above-described charging contact width portion of the charging roller with the photoreceptor. Further details are described hereinafter with reference to a background charging device illustrated in FIG. 4 which employs a charging roller cleaning member made of a sponge. In this background charging device, a charging roller 32 pressingly contacts a drum-shaped photoreceptor 31. The charging contact width of the charging roller 32 with the photoreceptor 31 in an axial direction of the charging roller 32 is indicated by a reference character Wch in FIG. 4 (hereinafter referred to as a charging roller width Wch). Further, a charging roller cleaning member 33 made of a sponge contacts the charging roller 32 and applies pressure along the axial direction of the charging roller 32 as indicated by double-headed arrow A in FIG. 4.
In this background charging device of FIG. 4, a length L1 of the charging roller cleaning member 33 along the axial direction of the charging roller 32 is set to be greater than the charging contact width Wch. Further, the charging contact width Wch is set to be greater than a width Wde of an effective development area in an axial direction of the photoreceptor 31 (hereinafter referred to as an effective development width Wde). The effective development area of the photoreceptor 31 is defined by diagonal lines in FIG. 4.
In the above-described background charging device, when a sequence of image forming steps are performed by an electrophotographic process, respective end portions 32a, 32b of the charging roller 32 are likely to be stained by scattered toner dropped from a cleaning device (not shown) of the image forming apparatus that removes residual toner remaining on the photoreceptor 31. As far as the scattered toner is not caused to enter a width of a part of the charging roller 32 corresponding to the effective development area of the photoreceptor 31, image quality is not deteriorated. However, when scattered toner such as an aggregate small amount of toner mass is dropped from the cleaning device on respective end portions 32a and 32b of the charging roller 32, and when the charging roller 32 is rotated by rotations of the photoreceptor 31, the aggregate small amount of toner mass may be pressed and spread by the pressure between the charging roller 32 and the charging roller cleaning member 33 into the width of the part of the charging roller 32 corresponding to the effective development area of the photoreceptor 31. Generally, the charging roller cleaning member 33 removes and holds foreign substances, such as toner and paper powder, from the surface of the charging roller 32, which are transferred onto the charging roller 32 from the photoreceptor 31. However, when a scattered toner such as an aggregated small amount of toner mass is dropped on the charging roller 32, the amount of toner exceeds a predetermined amount which can be held by the charging roller cleaning member 33, so that the charging roller cleaning member 33 cannot remove and hold the same therein. The toner remains on the charging roller 32 and is pressed and spread into the width portion of the part of the charging roller 32 corresponding to the effective development area of the photoreceptor 31 as described above. Then, the toner is fused on the surface of the charging roller 32 due to frictional heat and thereby adheres thereto. As a result, deterioration of charging property of the charging roller 32 is caused by the toner, and thereby deterioration of image quality, such as background fouling and density unevenness of toner image, occurs according to developing methods.
The present invention has been made in view of the above-discussed and other problems, and an object of the present invention is to address these problems.
The preferred embodiments of the present invention provide a novel charging device wherein deterioration of charging property of a charging roller due to a scattering toner can be prevented.
The preferred embodiments of the present invention provide a novel electrophotographic image forming process cartridge wherein deterioration of charging property of a charging roller due to a scattering toner can be prevented.
The preferred embodiments of the present invention provide a novel image forming apparatus wherein deterioration of charging property of a charging roller due to a scattering toner can be prevented.
These and other objects are achieved according to the present invention by providing a novel charging device for charging a photoreceptor of an image forming apparatus so that a latent image is formed thereupon to be developed by toner, the charging device including a charging roller that is configured to constantly contact the photoreceptor with a pressure so as to be rotated by rotations of the photoreceptor and that is configured to charge the photoreceptor, and a charging roller cleaning member that is configured to constantly contact a surface of the charging roller with a pressure so as to remove the toner transferred onto the charging roller from the photoreceptor. A length portion of the charging roller cleaning member along an axial direction of the charging roller is set to be equal to or greater than a width portion of an effective development area in an axial direction of the photoreceptor and smaller than a charging contact width of the charging roller with the photoreceptor in the axial direction of the charging roller.
According to another preferred embodiment of the present invention, a charging device for charging a photoreceptor of an image forming apparatus so that a latent image is formed thereupon to be developed by toner, includes a charging roller that is configured to constantly contact the photoreceptor with a pressure so as to be rotated by rotation of the photoreceptor and that is configured to charge the photoreceptor, and a charging roller cleaning member that is configured to constantly contact a surface of the charging roller with a pressure and to reciprocate in an axial direction of the charging roller so as to remove the toner transferred onto the charging roller from the photoreceptor. A maximum contact width portion of the charging roller cleaning member with the charging roller along the axial direction of the charging roller is set to be equal to or greater than a width portion of an effective development area in an axial direction of the photoreceptor and smaller than a charging contact width portion of the charging roller with the photoreceptor in the axial direction of the charging roller.
According to the present invention, the charging roller cleaning member may include a sponge material.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.